Microstructures such as microelectromechanical devices (hereafter MEMS devices) having deformable elements may suffer from device failure when the deformable elements deform plastically. Plastic deformation may be accumulated over operation time and result in residual plastic deformation at the natural resting state. The residual plastic deformation alters the operational states of the MEMS device—causing device failure. When such MEMS device is a member of an array of MEMS devices, the MEMS device may fail when one or more deformable elements of the MEMS devices in the array have residual plastic deformation more than a certain amount relative to the deformable elements of other MEMS devices in the array. Illumination of the deformable elements may accelerate such plastic deformation.
As a way of example, a micromirror device is a type of MEMS device. A typical micromirror device has a reflective mirror plate attached to a deformable hinge so as to move in response to an electrostatic field. In a digital operation, the mirror plate moves between an ON and OFF state corresponding to different rotation angles. In one example, the OFF state can be the natural resting state of the mirror plate; while the ON state can be a state where the mirror plate is moved a certain angle relative to the natural resting state. The deformable hinge deforms when the mirror plate is deflected; and residual plastic deformation may be developed when the deformable hinge is held at the deflected position over time. Such accumulated residual deformation, in turn, may alter an operation state, such as the natural resting state of the mirror plate, the OFF state, and/or the ON state, and may cause device failure when such alteration exceeds a certain amount. A micromirror device is often used as a member of an array of micromirror devices, such as a spatial light modulator. When one or more of the deformable hinges of the micromirror devices in the array have residual plastic deformation exceeding beyond a certain amount relative to the deformable hinges of other micromirror devices, the micromirror array device, i.e. the spatial light modulator fails.
Spatial light modulators are used in modulating light so as to transfer signals. Illumination of the deformable hinges in the spatial light modulator may accelerate the plastic deformation, which in turn, reduces the lifetime of the device.
Therefore, a method is desired for treating the deformable element of a MEMS device so as to improve the lifetime of the MEMS device.